Can we get caught by surprise by an asteroid?

We can get caught by surprise by an asteroid, but it's unlikely that one big enough to wipe us out will surprise us. Most of those have already been found, I believe.

However, the same can't be said about comets. Long period comets can come from any direction, and some can be big enough to do some serious damage.

 

Nope. They all come from the same direction.

Up.

 

I agree w/ you, but "unlikely" is not impossible, and part of the problem is that IF a big one pops up on everybody's radar screens tomorrow, and it is very big and it is going to hit us in, say, a year, do you think we could DO anything about it? Given a few years and an Apollo-project size commitment, we might be able to, but I wouldn't want to have to count on it.

 

You guyz heard that there's an asteroid fly by day after tomorrow, right? 2005 YU55. I guess that's what's prompted the OP's question.

 

Any idea what it would take to deflect or destroy an object of sufficient size to threaten Earth?

 

I think that's part of the problem. We DON'T know.

I HAVE read studies that show that just detonating a nuclear bomb on it isn't likely to do the trick if it's really big. I DOES seem that if we could put some kind of propulsive system on it LONG before it was due to hit us that we could drive it off course enought to miss

 

Massive object a year from colliding with earth?? The prognosis is unfavorable. 10 years, maybe. 1 year, very bad.

 

To answer the OP's 3 part question
1) Yes we can be surprised by an asteroid
2) no, we will not always find them with our telescopes before they hit us
3) no, the odds of being wiped out tomorrow are so low that no one would take that bet.

We are actually hit quite often. I think estimates have somewhere between 40k to 80k tons of material falling to the earth in a year. Most of it from dust sized particles.

For extinction event sized rocks it's far less frequent. And while we may be surprised, generally if something that large was heading to us there is a good probability that it'd be spotted.

What it would take to deflect or destroy the object? That would really depends on size, shape, composition, density, angle of attack, time to impact. If you can throw enough mass off the rock you can alter its course. The farther out the greater the course deviation.

We don't have anything that can do that today. Folks always talk "nukes". But our nuclear arsenal is designed to be a ballistic system and isn't suitable for "aiming into space". It would unlikely to be effective if that were the case at any rate.

 

If Bruce Willis is still alive during that time, I think 1 year would be more than enough...

How reflective are typical astroids? Is it probable that there is a very very dark astroid that is huge, so we wouldn't see it until it is too late?

 

This is one interesting talk regarding asteroid and possibility of defending earth against one:
http://www.ted.com/talks/phil_plait_how_to_defend_earth_from_asteroids.html

 

I think we do know. If you put delta V into an asteroid, then you can calculate the orbital effects.

If it's big enough then you are doomed. But if it's medium sized then it gets interesting.

A quick calculation shows that you aren't going to destroy the asteroid. The earth is tiny so that you just have to nudge it so that it misses. One thing that would be a big "oopps" is it would be a really bad thing if the asteroid was going to miss the earth and you nudged it so that it hits.

You could just paint half the asteroid so that solar radiation will nudge it.

 

Many asteroids are nothing more than rubble piles, as evidenced by their low density. Attempting to deflect them with a nuclear explosion would likely do no more than fragment them so that the Earth was subject to multiple large impacts rather than one very large impact.

 

Unless the explosion dispersed the mass of the asteroid to the extent that a significant amount of it missed the Earth altogether.

Additionally, even if it didn't, the same mass broken up into smaller chunks gives us a better chance of having much of it burn up in the atmo before causing surface damage.